Epitaxial liftoff techniques have been used since 1987 for achieving heterogeneous integration of many III-V and elemental semiconductor integrated circuits. For example, epitaxial liftoff has been shown to be effective for integrating hetero-junction bipolar transistors ("HBT's") and diode lasers on silicon, gallium arsenide and other common substrates. Despite this success, however, it has been impossible to integrate devices comprised of other important materials, namely non-semiconductor materials such as metal oxides, on these common substrates.
A need for integrated circuit devices combining non-semiconductor materials with conventional substrates has arisen in the field of electro-optic and magneto-optic communications. For example, a need has arisen for on-chip integrated magneto-optical devices, such as optical isolators, for use in fiber-optic telecommunications networks. Although commercially available isolators use bulk bismuth-substituted yttrium iron garnet ("Bi--YIG"), and other conventional integrated isolators require epitaxial growth on gadolinium gallium garnet ("GGG"), conventional epitaxial growth technologies are subject to the limitations of high temperature chemistry, complex stoichiometry and lattice matching.
More importantly, conventional methods are ineffective for growing single crystal-structures that exhibit good optical and magnetic properties for combination with semiconductor materials. Efforts using sputter growth technology for the growth of polycrystalline films, for example, have been unsuccessful in yielding single-crystal films with acceptable optical and magnetic properties.
Another need for integrated circuit devices combining non-semiconductor materials with conventional substrates has arisen in the field of microwave communications. For example, the need has arisen for frequency agile resonators requiring integrated circuit devices. Conventional frequency agile resonators, made of poly-crystalline materials such as ferroelectric solids, are undesirable because of their limited bandwidth and high loss tangents. Instead, it is desirable to construct frequency agile resonators and other integrated microwave circuits which are made of ferroelectric or magneto-optic single-crystal films.
Furthermore, conventional epitaxial liftoff techniques as developed for III-V semiconductors make use of the large differential etch rates between a buried sacrificial layer and the epitaxial structure of interest to detach the latter from its growth substrate. For example, early epitaxial liftoff techniques were based on the high wet etch selectivity of an aluminum arsenide ("AlAs") layer over an aluminum gallium arsenide ("Al.sub.x Ga.sub.1-x As") layer. Subsequent work has demonstrated the liftoff of epitaxially grown layers in other III-V materials, all based on selective etching of sacrificial epitaxial layers. Conventional bonding techniques for epitaxially grown layers have included the use of adhesives and van der Waals forces on bare substrates.
Therefore, it is an object of the present invention to provide a method for detaching micron-thin single-crystal films from crystal structures, such as epilayer/substrate or bulk metal oxide crystal structures, for bonding onto growth-incompatible substrates.
It is another object of the present invention to provide a method for detaching micron-thin single-crystal films made of magnetic garnet materials from growth-compatible substrates for use in integrated photonics and microwave circuits.
It is still another object of the present invention to provide a method for detaching micron-thin single-crystal films made of ferroelectric materials from growth-compatible substrates or bulk crystal structures for use in integrated photonics and microwave circuits.
It is yet another object of the present invention to provide a method for detaching micron-thin single-crystal films from growth-compatible substrates without using conventional etching techniques.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.